1. Field of the Invention
Aspects of the present invention relate to a solid proton conductor and a fuel cell including the solid proton conductor.
2. Description of the Related Art
An improved hydrogen conductive material for transmitting protons at high temperature under non- or low-humidified conditions is desirable for polymer electrolyte membrane fuel cells (PEMFCs).
A high-temperature electrolyte membrane can be prepared by removing a water component from an existing acid electrolyte membrane or using a hydrogen solvent having a high boiling point. It has been reported that when a fuel cell is fabricated using an phosphoric acid added to polybenzimidazole, the operational temperature of the fuel cell can increase up to about 200° C.
However, in this case, catalyst poisoning may be caused by the phosphoric acid, and the phosphoric acid can be washed out due to byproduct water when the PEMFC operates for a long time at a temperature of 100° C. or lower.
Heterocyclic compounds such as imidazoles, pyrazoles, and benzimidazoles have been developed as proton conductors capable of operating in a temperature range from about 150° C. to about 250° C. as a replacement for water (Journal of The Electrochemical Society, 2007, 154(4) 290-294).
It is known that such heterocyclic compounds have both amphoteric and autoprotolysis characteristics and can form a hydrogen bond network, thereby having hydrogen (proton) conductivity higher than that of water.
However, the heterocyclic compounds are volatile due to their relatively low molecular weight and flash point. Therefore, when a heterocyclic compound is used in a high-temperature fuel cell, it is necessary to maintain fluidity and mobility of hydrogen ions by directly fixing the heterocyclic compound to a polymer electrolyte membrane. Moreover, many additional synthesis processes are required to use the heterocyclic compound in a high-temperature fuel cell, and the yields of these processes are low.